Memory is indispensable for most modern electronic equipment, such as computers, personal digital assistants, cellular telephones and digital cameras. A memory device is widely used to retain computer programs or video/audio data. Furthermore, many applications require data to be stored in a non-volatile medium in order to fulfill the goal of portability. An example of non-volatile memory devices is flash memory, which is capable of retaining data when power is turned off. Flash memory is more competitive than conventional compact disks or magnetic-type recording media due to its light weight, superior recoding density, small form factor and shrinking cost. Flash memory has found many applications in the area of sensitive data access such as personal identity cards, healthcare cards, credit cards and electric wallets, and has widely replaced conventional paper or magnetic cards. However, there are still concerns in data protection for electronic cards. Hence, it may be desirable to strengthen the security measures for such non-volatile memory.